For some time now, it has been recognised that the simple use of rear-view mirrors to avoid collisions with vehicles that are attempting to overtake, or simply when they are changing lane, is clearly insufficient because of the existence of so-called blind angles of vision to which the driver does not have any direct or indirect visual access. For this reason various viewing alternatives to cover such blind angles have appeared based on different technologies, with the most representative relating to this invention, known to inventors covered by the following documents.
Patent application EP-A-0591743 described a device for the detection of relative positions between vehicles, by means of an optical sensor, preferably based on CCD technology, associated with a rear-view mirror casing, with said optical sensor associated with an electronic processing unit connected to a central information system in the vehicle, to which processed signals are sent, finally providing warning signals. The purpose of this device is to warn the driver of the vehicle in which it is installed of any possible risk of collision with another approaching vehicle via various signals (acoustic and luminous etc). There is also the possibility of using the cited device to warn the driver of the approaching vehicle of the possible risk of collision by switching on the vehicle's emergency or indicator lights. Although the proposal made in said document is very significant with respect to preventing collision with other vehicles, unlike that proposed by this invention, the employed system is based on the relative movement of said objects with respect to the vehicle in which the device is installed. Another disadvantage of the same is that the covered zone is not lateral, but instead to the rear, so that they detect objects that are moving within the zone on which the device is focused, which is generally installed in a rear-view mirror assembly, leaving a lateral zone of the vehicle that is neither visible to the driver nor covered by the device. In addition to this, the operation of this class of devices in low-visibility conditions (dazzling and fog etc) is clearly affected.
GB-A-2248692 proposes a MAD device for detecting the presence of a powerful magnet used to secure a bomb underneath a vehicle. Said proposal is based on the layout of a number of magnetic sensors underneath the vehicle, each of which provides an output in proportion to its respective magnetic field, which will vary when said bomb is attached to the vehicle by said powerful magnet, thus producing detection.
Patent application ES-A-2164568 proposes a detector for metal objects, particularly bombs, located in a vehicle, by analyzing variations in the magnetic filed caused in a circuit used as a detector by said object.
Although the last two cited background items propose the use of some means of detecting variations or distortions in the magnetic field produced by metal or magnetic objects (a bomb or its securing device) located inside or underneath a vehicle, it does not, at any time, mention the use of the same technique to detect vehicles in a blind angle of a vehicle, which are not visible to the driver of the same, neither directly nor via rear view mirrors, in order to avoid collisions between these during an overtaking or lane change operation.
Patent application WO-A-02/093529, belonging to the same applicant, describes a device for the detection of the presence of objects in a blind angle of a vehicle similar to the one proposed in this invention. Said objects contain, at least partly, ferromagnetic material which produces distortion in the earth's magnetic field. This device is mounted in an automobile vehicle with at least one blind angle and is able to detect an object located in the blind angle by employing some means of detecting distortion in the earth's magnetic field caused by the object. The invention further includes electronic and logic circuitry for processing and analyzing the electrical signals that are proportional to said magnetic field distortion obtained by the device, and based on the results of said analysis provide a warning to the vehicle's driver of any possible dangerous situation due to an invading object in the zone covered by the vehicle's blind angle, such as another vehicle attempting to overtake.
The solution proposed by patent WO-A-02/093529 represents a great advance in covering zones delimited by vehicle blind angles, above all when referring to the lateral zones of the same, with the proposed device being able to detect the same objects, whether moving or stationary and to differentiate them. This patent also suggests compensating the obtained measurements by means of said device, taking into account the influence of vehicle inclination, together with the distortion of the earth's magnetic field caused by the automobile vehicle itself. With respect to inclination, only the possibility of taking it into account when evaluating the detected values is indicated, and a device is claimed that measures the same, but at no time does it explain a method of implementation that uses the data obtained by the same device or how to compensate it for inclination. In relation to the internal vehicle distortions, it claims the fact of having calibration data that allows to discard from the signal produced by each magnetic sensor in the vehicle, the part corresponding to the distortion produced by the actual vehicle. However the method employed in obtaining these data, as described in the report (rotating the vehicle about its axis in the absence of any objects, to obtain values of the magnetic sensors installed in the vehicle), does not appear representative of all possible distortions of the earth's magnetic field that could be produced within the vehicle. One thing that is not considered at all in the document is the great influence that the trajectory adopted by the vehicle has on the earth's magnetic field, particularly during the route of a curve by the same, which will severely limit operation of the device proposed by the cited background if the vehicle is in the described situation within a curve.
It would therefore appear necessary to provide an alternative to the state of the art which, starting from patent WO-A-02/093529, substantially improves it and avoids the associated disadvantages because of a more realistic vision of the location in which the device is installed, the automobile vehicle. Such circumstances are not other than those of a moving object, having a trajectory and irregular behavior, not only due to the trajectory changes made by the driver, but also because of irregularities in the ground over which the vehicle is travelling that could include from significant ascending and descending slopes to varying sized potholes. This means a device that takes into account all errors that could be produced by the commented circumstances relating to distortion in the earth's magnetic field and, of course, compensate for them in the best possible fashion.